The invention relates to the field of torque converters and relates more particularly to a reactor intended for such torque converter and to a method for manufacturing it.
Torque converters which comprise a reactor, also known as a xe2x80x9cguide wheelxe2x80x9d, produced in the form of a moulded body which can be mounted around a reactor shaft via a freewheel are already known. This reactor is arranged coaxially between an impeller, also known as a pump wheel, and a turbine, also known as a turbine wheel, along one and the same axis.
These torque converters are used essentially in automatic transmissions of motor vehicles. The impeller is driven by the engine, while the turbine is connected to the vehicle transmission. The impeller and the turbine are produced in the form of cups facing each other and fitted with internal vanes, and between which an oil circulates under pressure, which oil may for example be a mineral oil or an oil of the DEXRON (trademark) type. The guide wheel also has vanes whose function is to straighten the fluids from the turbine and sent to the impeller. By virtue of its freewheel mechanism, the reactor may either be stationary or driven in rotation, but in just one direction.
There are currently two main techniques for manufacturing torque converter reactors.
Known first of all are aluminium reactors made by an injection-moulding technique which has the disadvantage of entailing subsequent machining work. Furthermore, these reactors are made in steel moulds which rapidly corrode and which therefore have to be replaced frequently.
Also known are reactors made of thermoset produced by an injection-compression moulding technique which entails baking each component in a mould, thus lengthening the cycle time. Furthermore, these thermosets do not allow the overmoulding of large-sized rigid inserts because they have a tendency to crack when they shrink around this type of insert.
The invention provides another solution to the problem of producing torque converter reactors.
For that purpose it proposes a reactor for a torque converter in which the body of the reactor is made of thermoplastic and is overmoulded around an outer ring that the freewheel comprises so that the thermoplastic covers an outer annulus of the outer ring and at least one annular face of the outer ring on the same side as the turbine.
Thermoplastics, unlike thermosets, have the advantage of having a long elongation at rupture, which allows them, in spite of the shrinkage, to accept the overmoulding of large-sized inserts without cracking.
In addition, overmoulding the outer ring of the freewheel makes it possible to maintain its as-produced outside diameter, thus reducing its cost. Furthermore, the earlier technologies, in which the ring is mounted in the reactor rather than overmoulded, dictate a need to have a precise bore in the reactor for the insertion of the ring and a precise outside diameter on the ring and, finally, in most cases, a thrust bearing on the turbine side (or on the impeller side) that can be removed so as to engage the ring in the reactor. All these specific requirements explain the higher cost of production of the assembly of the prior art.
Furthermore, a reactor for a torque converter comprises vanes each having a leading edge facing towards the turbine and a trailing edge facing towards the impeller. The invention anticipates that the trailing edge of each of the vanes is truncated at the time of moulding. This design allows the vanes to be mounted closer together and also makes it possible to reduce the risk of weakening of the trailing edges.
Other additional or alternative features of the reactor of the invention are as follows:
the body comprises an axial thrust bearing on the same side as the impeller and an axial thrust bearing on the same side as the turbine, at least one of these axial thrust bearings being moulded with the body;
the axial thrust bearing on the same side as the impeller and the axial thrust bearing on the same side as the turbine are moulded with the body, and the axial thrust bearing on the same side as the turbine is radially offset from the axis to allow direct mounting of the freewheel;
the axial thrust bearing on the same side as the impeller and the axial thrust bearing on the same side as the turbine each comprise radial lubricating and/or cooling ducts running in a generally radial direction;
the body comprises a bearing for rotational guidance about the reactor shaft, this bearing being equipped with axial lubricating and/or cooling ducts running in a generally axial direction and corresponding angularly with the radial lubricating and/or cooling ducts of the axial thrust bearing on the same side as the impeller;
the axial thrust bearing on the same side as the impeller is a needle thrust bearing, while the axial thrust bearing on the same side as the turbine is moulded with the body;
the needle thrust bearing comprises an inner cheek mechanically anchored in the plastic of the body by anchoring means and an outer cheek pressed against the impeller;
the inner cheek bears against an annular part of the body, which annular part bears against the outer ring;
the inner cheek bears against an annular part of the outer ring which extends as far as the reactor shaft;
the body is equipped with a flanged thrust bearing, made up of a cylindrical bush extended by a flange, forming a thrust bearing via its flange and a bearing via its bush, this flanged thrust bearing advantageously being made of a self-lubricating material so as to allow sliding on the impeller hub and the reactor shaft;
the body comprises retaining clips formed by moulded-in bosses projecting radially towards the axis to come into abutment against flexible elements of an outer cage of the freewheel, which is accommodated in the outer ring;
the outer ring is metallic, advantageously made of steel, and has reliefs of chosen shape, particularly knurling or corrugations, produced on the outer annulus of the outer ring and over which the plastic of the body is moulded.
In another aspect, the invention relates to a torque converter comprising a reactor arranged coaxially between an impeller and a turbine, the reactor being as defined hereinabove.